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[BranchFolding] Merge debug locs on common hoisted code
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‎llvm/lib/CodeGen/BranchFolding.cpp

Lines changed: 28 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2071,7 +2071,34 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
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if (!HasDups)
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return false;
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2074-
MBB->splice(Loc, TBB, TBB->begin(), TIB);
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// Hoist the instructions from [T.begin, TIB) and then delete [F.begin, FIB).
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// Merge the debug locations. FIXME: We should do something with the
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// debug instructions too (from BOTH branches).
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{
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// TIB and FIB point to the end of the regions to hoist/merge in TBB and
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// FBB.
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MachineBasicBlock::iterator FE = FIB;
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MachineBasicBlock::iterator FI = FBB->begin();
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for (MachineBasicBlock::iterator TI :
2083+
make_early_inc_range(make_range(TBB->begin(), TIB))) {
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// Move debug instructions and pseudo probes without modifying them.
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// FIXME: This is the wrong thing to do for debug locations, which
2086+
// should at least be killed.
2087+
if (TI->isDebugOrPseudoInstr()) {
2088+
TI->moveBefore(&*Loc);
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continue;
2090+
}
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// Get the next non-meta instruction in FBB.
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FI = skipDebugInstructionsForward(FI, FE, false);
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assert(FI != FE && "Expected non-debug lockstep");
2095+
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// Merge debug locs on hoisted instructions.
2097+
TI->setDebugLoc(
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DILocation::getMergedLocation(TI->getDebugLoc(), FI->getDebugLoc()));
2099+
TI->moveBefore(&*Loc);
2100+
}
2101+
}
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FBB->erase(FBB->begin(), FIB);
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20772104
if (UpdateLiveIns)

‎llvm/test/DebugInfo/X86/branch-folder-dbg.mir

Lines changed: 111 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,111 @@
1+
# RUN: llc %s --start-before=branch-folder --stop-after=branch-folder -o - | FileCheck %s
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## Check that common instructions hoisted from `if.then` and `if.else` into
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## common pred `entry` get merged debug locations.
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## FIXME: The debug instructions handling here is wrong.
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# CHECK: bb.0
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# CHECK: CALL64pcrel32 @f, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
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## --- Start splice from bb.2.if.else ---
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# CHECK-NEXT: DBG_VALUE 2, $noreg, ![[#]], !DIExpression(), debug-location ![[#]]
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# CHECK-NEXT: $edi = MOV32r0 implicit-def dead $eflags, debug-location !DILocation(line: 0, scope: ![[#]])
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## --- End splice --------------
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# CHECK-NEXT: TEST64rr killed renamable $rax, renamable $rax, implicit-def $eflags
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# CHECK-NEXT: JCC_1 %bb.2, 9, implicit killed $eflags
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# CHECK: bb.1
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--- |
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target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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declare dso_local noundef i64 @f() local_unnamed_addr
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define dso_local noundef i32 @g() local_unnamed_addr !dbg !7 {
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%call = tail call noundef i64 @f()
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%cmp1 = icmp sgt i64 0, %call
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%conv2 = trunc i64 0 to i32
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br i1 %cmp1, label %if.then, label %if.else
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if.then: ; preds = %0
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#dbg_value(i64 0, !11, !DIExpression(), !13)
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tail call void @_Z3fooii(i32 noundef %conv2, i32 noundef 0), !dbg !14
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#dbg_value(i64 1, !11, !DIExpression(), !13)
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br label %if.end, !dbg !15
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if.else: ; preds = %0
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#dbg_value(i64 2, !11, !DIExpression(), !13)
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tail call void @_Z3barii(i32 noundef %conv2, i32 noundef 1), !dbg !16
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#dbg_value(i64 3, !11, !DIExpression(), !13)
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br label %if.end, !dbg !17
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if.end: ; preds = %if.else, %if.then
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ret i32 2
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}
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declare void @_Z3fooii(i32 noundef, i32 noundef) local_unnamed_addr
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declare void @_Z3barii(i32 noundef, i32 noundef) local_unnamed_addr
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!llvm.module.flags = !{!0, !1}
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!llvm.ident = !{!2}
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!llvm.dbg.cu = !{!3}
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!llvm.debugify = !{!5, !6}
54+
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!0 = !{i32 7, !"Dwarf Version", i32 5}
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!1 = !{i32 2, !"Debug Info Version", i32 3}
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!2 = !{!"clang version 21.0.0"}
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!3 = distinct !DICompileUnit(language: DW_LANG_C, file: !4, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
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!4 = !DIFile(filename: "test.nodbg.ll", directory: "/")
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!5 = !{i32 15}
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!6 = !{i32 7}
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!7 = distinct !DISubprogram(name: "g", linkageName: "g", scope: null, file: !4, line: 1, type: !8, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !3, retainedNodes: !10)
63+
!8 = !DISubroutineType(types: !9)
64+
!9 = !{}
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!10 = !{!11}
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!11 = !DILocalVariable(name: "1", scope: !7, file: !4, line: 3, type: !12)
67+
!12 = !DIBasicType(name: "ty64", size: 64, encoding: DW_ATE_unsigned)
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!13 = !DILocation(line: 3, column: 1, scope: !7)
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!14 = !DILocation(line: 9, column: 1, scope: !7)
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!15 = !DILocation(line: 10, column: 1, scope: !7)
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!16 = !DILocation(line: 11, column: 1, scope: !7)
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!17 = !DILocation(line: 12, column: 1, scope: !7)
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...
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---
75+
name: g
76+
body: |
77+
bb.0 (%ir-block.0):
78+
successors: %bb.1(0x40000000), %bb.2(0x40000000)
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frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp
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frame-setup CFI_INSTRUCTION def_cfa_offset 16
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CALL64pcrel32 @f, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
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TEST64rr killed renamable $rax, renamable $rax, implicit-def $eflags
84+
JCC_1 %bb.2, 9, implicit killed $eflags
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JMP_1 %bb.1
86+
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bb.1.if.then:
88+
successors: %bb.3(0x80000000)
89+
90+
DBG_VALUE 0, $noreg, !11, !DIExpression(), debug-location !13
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$edi = MOV32r0 implicit-def dead $eflags, debug-location !14
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$esi = MOV32r0 implicit-def dead $eflags, debug-location !14
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CALL64pcrel32 target-flags(x86-plt) @_Z3fooii, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit killed $esi, implicit-def $rsp, implicit-def $ssp, debug-location !14
94+
DBG_VALUE 1, $noreg, !11, !DIExpression(), debug-location !13
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JMP_1 %bb.3, debug-location !15
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97+
bb.2.if.else:
98+
successors: %bb.3(0x80000000)
99+
100+
DBG_VALUE 2, $noreg, !11, !DIExpression(), debug-location !13
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$edi = MOV32r0 implicit-def dead $eflags, debug-location !16
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$esi = MOV32ri 1, debug-location !16
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CALL64pcrel32 target-flags(x86-plt) @_Z3barii, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit killed $esi, implicit-def $rsp, implicit-def $ssp, debug-location !16
104+
DBG_VALUE 3, $noreg, !11, !DIExpression(), debug-location !13
105+
106+
bb.3.if.end:
107+
$eax = MOV32ri 2
108+
$rcx = frame-destroy POP64r implicit-def $rsp, implicit $rsp
109+
frame-destroy CFI_INSTRUCTION def_cfa_offset 8
110+
RET 0, $eax
111+
...

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